MoS_(2) nanoflowers coupled with ultrafine Ir nanoparticles for efficient acid overall water splitting reaction

Bi-functional electrocatalysts for acid overall water splitting reactions are crucial but still challenging to the development of proton exchange membrane water electrolysis.Herein,an efficient bi-functional catalyst of Ir/MoS_(2) nanoflowers(Ir/MoS_(2) NFs) catalyst was reported for acidic water electrolysis which can be constructed by coupling three-dimensionally interconnected MoS_(2) NFs with ultrafine Ir nanoparticles.A more suitable adsorption ability for the H* and *OOH intermediates was revealed,where the Ir sites were proposed as the main active center and MoS_(2) promoted the charge relocation to electronically modify the interfacial structure.The significant interfacial charge redistribution between the MoS_(2) NFs and the Ir active sites synergistically induced excellent catalytic activity and stability for the water electrolysis reaction.Specifically,the catalyst required overpotentials of 270 and 35 mV to reach a kinetic current density of 10 mA cm^(-2)for OER and HER,respectively,loading on the glass carbon electrode,with high catalytic kinetics,stability,and catalytic efficiency.A two-electrode system constructed by Ir/MoS_(2) NFs drove 10 mA cm^(-2)at a cell voltage of 1.55 V,about 70 mV lower than that of the commercial Pt/C||IrO_(2) system.In addition,partial surface oxidation of Ir nanoparticles to generate high-valent Ir species was also found significant to accelerate OER.The enhanced catalytic performance was attributed to the strong metal-support interaction in the Ir/MoS_(2) NFs catalyst system that changed the electronic structure of Ir metal and promoted the synergistic catalytic effect between Ir and MoS_(2) NFs.The work presented a novel platform of Ir-catalyst for proton exchange membrane water electrolysis.

Hydrogen peroxide biosensor based on electrodeposition of zinc oxide nanoflowers onto carbon nanotubes film electrode

A new amperometric biosensor for hydrogen peroxide was developed based on adsorption of horseradish peroxidase at the glassy carbon electrode modified with zinc oxide nanoflowers produced by electrodeposition onto multi-walled carbon nanotubes （MWNTs） film. The morphology of the MWNTs/nano-ZnO electrode has been investigated by scanning electron microscopy （SEM）, and the electrochemical performance of the electrode has also been studied by amperometric method. The resulting electrode offered an excellent detection for hydrogen peroxide at -0.11 V with a linear response range of 9.9×10^-7 to 2.9×10^-3 mol/L with a correlation coefficient of 0.991, and response time 〈5 s. The biosensor displays rapid response and expanded linear response range, and excellent stability.

3D MoS_(2)/graphene nanoflowers as anode for advanced lithium-ion batteries

Vertical MoS2nanosheets were controllably patterned onto graphene as nanoflowers through a two-step hydrothermal method. The interconnected network and intimate contact between MoS2nanosheets and graphene by vertical channels enabled a high mechanical integrity of electrode and cycling stability. In particular, MoS2/graphene nanoflowers anode delivered an ultrahigh specific capacity of 901.8 mA·h/g after 700 stable cycles at 1000 mA/g and a corresponding capacity retention as 98.9% from the second cycle onwards.

Graphene quantum dots decorated rutile TiO_2 nanoflowers for water splitting application

Flower like rutile TiO_2 films were decorated with green-photoluminescent graphene quantum dots（GQDs） and photovoltaic properties were investigated for water splitting application. Rutile TiO_2 nanoflowers（NFs） and GQDs（average width of^12 nm） synthesized separately using a hydrothermal method and TiO_2 NFs were decorated with various amounts of GQDs solution（x = 5, 10, 15 and 20 μL） by spin coating. Optical characterization reveals that GQDs are highly luminescent and absorb UV and visible light photons with wavelengths up to 700 nm. GQDs-x/TiO_2 electrode shows a photocurrent enhancement of ~95% compared to pristine TiO_2 NFs for the optimum sample（x = 15 μL） at an applied potential of P = 0 V using 1 M Na_2SO_4 solution as electrolyte.

Self-assembled MoS_(2)/C nanoflowers with expanded interlayer spacing as a high-performance anode for sodium ion batteries

Two-dimensional(2D)MoS_(2) nanomaterials have been extensively studied due to their special structure and high theoretical capacity,but it is still a huge challenge to improve its cycle stability and achieve superior fast charge and discharge performance.Herein,a facile one-step hydrothermal method is proposed to synthetize an ordered and self-assembled MoS_(2) nanoflower(MoS_(2)/C NF)with expanded interlayer spacing via embedding a carbon layer into the interlayer.The carbon layer in the MoS_(2) interlayer can speed the transfer of electrons,while the nanoflower structure promotes the ions transport and improves the structural stability during the charging/discharging process.Therefore,MoS_(2)/C NF electrode exhibits exceptional rate performance(318.2 and 302.3 mA·h·g^(-1) at 5.0 and 10.0 A·g^(-1),respectively)and extraordinary cycle durability(98.8%retention after 300 cycles at a current density of 1.0 A·g^(-1)).This work provides a simple and feasible method for constructing high-performance anode composites for sodium ion batteries with excellent cycle durability and fast charge/discharge ability.

Novel P-doping-tuned Pd nanoflowers/S,N-GQDs photo-electrocatalyst for high-efficient ethylene glycol oxidation

Traditional photo-electcatalyst structures of small noble metal nanoparticles assembling into large-scale photoactive semiconductors still suffer from agglomeration of noble metal nanoparticles,insufficient charge transfer,undesirable photoresponse ability that restricted the photo-electrocatalytic performance.To this end,a novel design strategy is proposed in this work,namely integrating small-scale photoactive materials(doped graphene quantum dots,S,N-GQDs)with large-sized noble metal(Pd P)nanoflowers to form novel photo-electrocatalysts for high-efficient alcohol oxidation reaction.As expected,superior electrocatalytic performance of Pd P/S,N-GQDs for ethylene glycol oxidation is acquired,thanks to the nanoflower structure with larger specific surface area and abundant active sites.Furthermore,nonmetal P are demonstrated,especially optimizing the adsorption strength,enhancing the interfacial contact,reducing metal agglomeration,ensuring uniform and efficient doping of S,N-GQDs,and ultimately significantly boost the catalytic activity of photo-electrocatalysts.

Aptamer-induced in-situ growth of acetylcholinesterase-Cu_(3)(PO_(4))_(2)hybrid nanoflowers for electrochemical detection of organophosphorus inhibitors

Enzyme-inorganic hybrid nanoflowers(HNFs)have shown excellent sensing capabilities due to their large specific surface area as well as the simplicity and mildness of the preparation process.However,coupling HNFs to electrodes to fabricate a uniform and controllable enzymatic electrochemical sensing interface remains a challenge.Here,we proposed an aptamer-induced insitu fabrication strategy for preparing an HNF-based electrochemical sensor with ideal performance.Central to this strategy is the introduction of acetylcholinesterase(AChE)-specific binding aptamer(Apt),which induces the in-situ growth of AChE-copper phosphate(Cu_(3)(PO_(4))_(2))HNFs on the surface of carbon paper(CP).In addition,a dense gold nanoparticle(AuNP)layer was electrodeposited on the CP for anchoring Apt and further extending the electroactive surface area.The prepared AChECu_(3)(PO_(4))_(2)HNF/Apt/AuNP/CP biosensor exhibited a wide detection range from 1 to 107 pM for the four organophosphorus inhibitors,including isocarbophos,dichlorvos,methamidophos,and parathion,with detection limits down to 0.016,0.028,0.071,and 0.113 pM,respectively.With the reactivation of pralidoxime chloride,the electrode can still recover 98.1%of the response after five times of repeated use.In real sample detection,the biosensor achieved high recoveries from 96.45%to 100.13%.The detection target may be extendable to other AChE inhibitors(e.g.,drugs for Alzheimer’s disease).This study demonstrates for the first time the feasibility of using aptamers as an inducer to fabricate an electrochemical enzyme sensing interface in-situ.This strategy can be used to fabricate other enzyme-based biosensors and therefore has broader applications.

An intravascular needle coated by ZnO nanoflowers for in vivo elimination of circulating tumor cells

Circulating tumor cells(CTCs)are recognized as the main source of tumor recurrence and metastasis.Eliminating the CTCs in peripheral blood provides a new strategy to reduce the probability of recurrence or metastasis.Here,we proposed a concept to eliminate CTCs by inserting a needle in the superficial blood vessel.Using the property of ZnO and the structure of nanoflowers,we designed a medical needle coated with ZnO nanoflowers(ZNFs),which killed about 90%of captured CTCs in vitro and prevented the injecting CTCs from spreading to lung tissue in BABL/c mouse model.Results in vitro and in vivo demonstrated that the CTCs not only were captured and killed,but also detached from the needle surface after dead,enabling the ZNFs needle continually eliminate CTCs.Furthermore,a theoretical model was presented to explain the penetration mechanism of cells by nanostructures,which indicated that nanoflowers structure can puncture CTCs more easily than vertical nanowire structure.The concept of inserting an intravascular needle provides a potential strategy to lower the concentration of CTCs in blood and reduce the probability of tumor recurrence or metastasis.

2D Ti_(3)C_(2)T_(x)MXene-derived self-assembled 3D TiO_(2)nanoflowers for nonvolatile memory and synaptic learning applications

Two-dimensional(2D)semiconducting materials and transition-metal oxides are promising materials for nonvolatile memory and brain-inspired neuromorphic computing applications.However,it remains chal-lenging to obtain high-quality stacked 2D films with low energy consumptions(or drive currents)be-cause of their high interfacial resistance.In this study,we synthesized 2D Ti_(3)C_(2)T_(x)MXene-derived three-dimensional(3D)TiO_(2)nanoflowers(NFs)as a feasible resistive switching(RS)material with outstanding electronic properties and synaptic learning capabilities.The electrical and optical characteristics of the synthesized material were determined through density functional theory calculations.Electrical measure-ments of the Al/Ti_(3)C_(2)T_(x)-TiO_(2)NF/Pt memory device indicated the occurrence of forming-free switching phenomena with extremely low switching voltages(0.68-0.53 V),stable ON/OFF ratio(2.3×103),and retention greater than 105 s.The Holt-Winters exponential smoothing technique was used for mod-eling and predicting the switching voltages of the RS device.The mechanism underlying the reliable RS was confirmed by observing the dense conductive filaments through conductive atomic force mi-croscopy.Interestingly,the 2D Ti_(3)C_(2)T_(x)MXene-derived 3D TiO_(2)NF-based RS device mimicked the po-tentiation/depression and spike-time-dependent plasticity of a biological synapse.Finally,a convolutional neural network was implemented based on the observed synaptic weights of Al/Ti_(3)C_(2)T_(x)-TiO_(2)NF/Pt for image-edge detection.

Rare earth(Gd,La) co-doped ZnO nanoflowers for direct sunlight driven photocatalytic activity

In this work Gd/La@ZnO nanoflower photocatalyst was successfully synthesized by a co-precipitation method and applied for rhodamine B(Rh B) and tetracycline(TCN) degradation under direct sunlight irradiation.The doping of rare earth elements extends the optical absorption wavelength of ZnO from UV region(390 nm) to visible-light region(401 nm).In addition,the co-doped ZnO nanoflower exhibits a lower charge recombination efficiency which was confirmed by photoluminescence emission analysis.Moreover,the co-doped ZnO nanoflower exhibits the maximum degradation efficiency of 91% for Rh B and 74% for TCN under sunlight irradiation.The calculated synergistic index of co-doped ZnO is higher than that of the pure ZnO.Reactive radicals’ production was confirmed by terephthalic acid(TA) and nitro-blue tetrazolium(NBT) tests.The holes and hydroxyl(·OH) radicals play the major role in degradation reaction and it was confirmed by scavenger’s test.Moreover,the recycling test confirms the stability of the photocatalyst.

Gold nanoflowers for 3D volumetric molecular imaging of tumors by photoacoustic tomography

By binding molecular probes that target tumor cells, gold nanoparticles （AuNPs） with superior characteristics have shown great potential in tumor molecular imaging studies. The non-invasive, high-resolution, and three-dimensional imaging of the targeted AuNPs within the tumor is desirable for both diagnosis and therapy. In this study, gold nanoflowers （AuNFs） are presented as a novel contrast agent for photoacoustic tomography （PAT）. By binding to folic acid, the molecular probe, the tail-vein injected AuNFs concentrated within the tumor site in mice; this was clearly visualized by three-dimensional （3D） PAT imaging. In addition, toxicity assay proved that AuNFs were harmless to living cells and animals. Our results demonstrate that AuNFs have great potential in tumor molecular imaging.

Facile self-template fabrication of hierarchical nickel-cobalt phosphide hollow nanoflowers with enhanced hydrogen generation performance

Developing facile methods to construct hierarchical-structured transition metal phosphides is beneficial for achieving high-efficiency hydrogen evolution catalysts.Herein,a self-template strategy of hydrothermal treatment of solid Ni-Co glycerate nanospheres followed by phosphorization is delivered to synthesize hierarchical Ni Co P hollow nanoflowers with ultrathin nanosheet assembly.The microstructure of Ni Co P can be availably tailored by adjusting the hydrothermal treatment temperature through affecting the hydrolysis process of Ni-Co glycerate nanospheres and the occurred Kirkendall effect.Benefitting from the promoted exposure of active sites and affluent mass diffusion routes,the HER performance of the Ni Co P hollow nanoflowers has been obviously enhanced in contrast with the solid Ni Co P nanospheres.The fabricated Ni Co P hollow nanoflowers yield the current density of 10 m A cmà2at small overpotentials of 95 and 127 m V in 0.5 mol Là1H2SO4and 1.0 mol Là1KOH solution,respectively.Moreover,the two-electrode alkaline cell assembled with the Ni Co P and Ir/C catalysts exhibits sustainable stability for overall water splitting.The work provides a simple but efficient method to regulate the microstructure of transition metal phosphides,which is helpful for achieving high-performance hydrogen evolution catalysts based on solid-state metal alkoxides.

CuO nanoflowers/copper fiber felt integrated porous electrode for lithium-ion batteries

The structure of current collectors has significant effects on the performance of a lithium-ion battery(LIB).In this study,we use copper fiber felts made by multi-tooth cutting and high-temperature solid-phase sintering as the current collector for LIBs.An integrated porous electrode based on CuO nanoflowers/copper fiber felt is developed for the anode.Results suggest that the reversible capacity and cycle stability of this new anode are significantly improved,compared with the pristine bare-surface copper plate under the same condition of rate cycles.The new anode structure based on the copper-fiber felt with a porosity of 60%exhibits a higher performance with an initial specific capacity of 609.5 mAh g^(-1)and retains 486.1 mAh g^(-1)after 200 cycles at a current density of 0.5 C.The improved electrochemical performance of this electrode is attributed to its large surface area of CuO nanoflowers and porous structure of the copper fiber felt,due to enhanced contact between the active material of CuO nanoflowers and electrolyte.This pore-rich structure makes the electrolyte easy to permeate into the electrode,shortens the diffusion path of Li^(+),reduces the internal resistance and alleviates the volume expansion of the active material during the insertion and desertion processes of Li^(+).

Thermal transformation of δ-MnO_2 nanoflowers studied by in-situ TEM

ln-situ transmission electron microscopy in combination with a heating stage has been employed to real-time monitor varia- tions of δ-phase MnO2 nanoflowers in terms of their morphology and crystalline structures upon thermal annealing at elevated temperatures up to -665 ℃. High-temperature annealing drives the diffusion of the small δ-MnO2 nanocrystallites within short distances less than 15 nm and the fusion of the adjacent δ-MnO： nanocrystallites, leading to the formation of larger crystalline domains including highly crystalline nanorods. The annealed nanoflowers remain their overall flower-like morphology while they are converted to α-MnO2. The preferred transformation of the δ-MnO2 to the α-MnO2 can be ascribed to the close lattice spacing of most crystalline lattices between δ-MnO2 and α-MnO2, that might lead to a possible epitaxial growth of ct-MnO2 lattices on the 8-MnO2 lattices during the thermal annealing process.

Facile synthesis of gold nanoflowers as SERS substrates and their morphological transformation induced by iodide ions

We report a new strategy to prepare gold nanoflowers （AuNFs） using a two-step seed-mediated method. The as-prepared AuNFs were employed as surface-enhance Raman scattering （SERS） substrates, showing strong signal enhancement. We further found that iodide ions （I^-） could selectively induce the morphological transformation of AuNFs to spheres, resulting in a blue-shift of the localized surface plasmon resonance （LSPR） bands, a color change of the AuNFs solution from blue to red, and decreased SERS activity. This behavior allows the AuNFs to be used in the determination of I^-.

Palladium nanoflowers supported on amino-fullerene as novel catalyst for reduction of 4-nitrophenol

In this study,we report the synthesis of novel palladium nanoflowers(Pd NFs)on amino-functionalized fullerene(C60-NH2)by hydrothermal self-assembly growth using ethylenediamine(EA)as a functional reagent.The successful formation of Pd nanoflowers supported amino-functionalized fullerene(C60-NH2/Pd NFs)is evidenced by UV-vis and powder X-ray diffraction(XRD).The morphology of Pd NFs over the C60-NH2 surface has been investigated by high-resolution transmission electron microscopy(TEM)and Fourier-transform infrared(FT-IR)techniques.The supported Pd nanoflowers(Pd NFs/C60-NH2)exhibit remarkably superior catalytic activity toward the reduction of 4-nitrophenol(4-NP).It exhibits remarkable UV-vis spectra response from 4-nitrophenol to 4-aminophenol(4-AP)(99%in 2.0 min)with a turnover frequency of 12.35 min^-1.Its excellent catalytic stability and durability offer the promising application in catalysis.

Self-assembling, pH-responsive nanoflowers for inhibiting PAD4 and neutrophil extracellular trap formation and improving the tumor immune microenvironment

Self-assembling carrier-free nanodrugs are attractive agents because they accumulate at tumor by an enhanced permeability and retention(EPR) effect without introduction of inactive substances,and some nanodrugs can alter the immune environment. We synthesized a peptidyl arginine deiminase 4(PAD4) molecular inhibitor, ZD-E-1 M. It could self-assembled into nanodrug ZD-E-1. Using confocal laser scanning microscopy, we observed its cellular colocalization, PAD4 activity and neutrophil extracellular traps(NETs) formation. The populations of immune cells and expression of immune-related proteins were determined by single-cell mass cytometry. ZD-E-1 formed nanoflowers in an acidic environment, whereas it formed nanospheres at pH 7.4. Accumulation of ZD-E-1 at tumor was pHresponsive because of its pH-dependent differences in the size and shape. It could enter the nucleus and bind to PAD4 to prolong the intracellular retention time. In mice, ZD-E-1 inhibited tumor growth and metastasis by inhibiting PAD4 activity and NETs formation. Besides, ZD-E-1 could regulate the ratio of immune cells in LLC tumor-bearing mice. Immunosuppressive proteins like LAG3 were suppressed,while IFN-γ and TNF-a as stimulators of tumor immune response were upregulated. Overall, ZD-E-1 is a self-assembling carrier-free nanodrug that responds to pH, inhibits PAD4 activity, blocks neutrophil extracellular traps formation, and improves the tumor immune microenvironment.

Dual-selective detection of CO and CH_(4) based on hierarchical porous In_(2)O_(3) nanoflowers with Pd modification

The timely and effective detection of CO and CH_(4) is critical as the explosion and poisoning of them can bring serious potential risks to coal mining.In this study,combining metal oxide semiconductors with noble metals offers a promising route to achieve this target.Hierarchical porous Pd modified In_(2)O_(3) nanoflowers were prepared via two-step hydrothermal method and exhibited dual detection of CO and CH_(4) at different temperatures.The material has been characterized by a number of advanced techniques and the results indicate that Pd modified In_(2)O_(3) are hierarchical porous nanoflowers structure consisting of pores of approximately 1.8 nm in size.The sensing properties results show that the Pd modified In_(2)O_(3) based sensor exhibits temperature-dependent dual selectivity detection of CO at 280℃ and CH_(4) at 340℃.In addition,the Pd modified In_(2)O_(3) sensor display higher sensing response of CO(5.824 for 100 ppm)and CH_(4)(1.162 for 1000 ppm),fast response and recovery time,as well as good repeatability,which demonstrating the great potential for practical application.Such good gas-sensing performance are mainly attributed to the unique flower-like structure,the presence of porosity on the sample surface,and the catalytic effect of Pd.

Hierarchical SnO_2 nanoflowers assembled by atomic thickness nanosheets as anode material for lithium ion battery

Hierarchical SnO2 nanoflowers assembled by atomic thickness nanosheets were prepared by facile one-pot solvothermal method with acetone/water mixture as solvent. The crystal structure, morphology and the microstructure of the as-prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and atomic force microscope （AFM）. Results revealed that the nanoflowers （2-4 μm） were assembled by the ultrathin SnO2 nanosheets （3.1 nm esti- mated by AFM）. When tested as anode material for lithium ion batteries, the SnO2 nanoflowers showed improved cy- cling stability comparing with the commercial SnO2 parti- cles. The reversible charge capacity of SnO2 nanoflowers maintained 350.7 mAh/g after 30 cycles, while that of the commercial SnO2 was only 112.2 mAh/g. The high re- versible capacity and good cycling stability could be ascri- bed to the hierarchical nanostructure, atomic thickness nanosheets and large surface area of the SnO2 nanoflowers.

Highly selective electrochemical method for the detection of serotonin at carbon fiber microelectrode modified with gold nanoflowers and overoxidized polypyrrole

A highly selective and sensitive electrochemical method was developed for the detection of serotonin (5-hydroxytryptamine, 5-HT) at gold nanoflowers (Au NFs) and overoxidized polypyrrole (OPPy) modified carbon fiber microelectrode (CFME). Carbon fiber was firstly modified with gold nanoflowers using electroless deposition method, and then modified with overoxidized polypyrrole using electrochemical polymerization and overoxidization to obtain OPPy/Au NFs/CFME. The obtained OPPy/Au NFs/CFME was characterized by field emission scanning electron microscopy and electrochemical techniques. It was found that the OPPy/Au NFs/CFME showed good sensitivity for the detection of 5-HT in the range of 10 nmol/L-7.0μmol/L with detection limit of 2.3 nmol/L, and negligible interferences from ascorbic acid, 5-hydroxyindole acetic acid and uric acid. The OPPy/Au NFs/CFME was successfully applied to the detection of 5-HT in human serum samples with good recovery. The work demonstrates that the electrochemical method, incorporating signal amplification of Au NFs with higher cation selection of OPPy, provides a promising tool for the detection of 5-HT in biological systems.